Liquefied Natural Gas (LNG) is a clean, viable source of heat and power. When natural gas is cooled and liquefied, the density increases about 600 times. In other words, LNG occupies about 1/600th the volume or space than the same volume of natural gas vapor. LNG is, accordingly, easier to transport, and far more energy dense than natural gas in a vapor form. Liquefying natural gas into LNG, however, requires a significant amount of energy and special cryogenic tanks are needed to prevent rapid heat gain after the natural gas is liquefied.
When natural gas is liquefied into LNG, the energy content becomes more comparable to other liquid fuels. Nonetheless, as illustrated below, LNG generally provides less energy per gallon as compared to other fuels (measured in British Thermal Units (Btu)):
One gallon diesel=135,000 Btu
One gallon gasoline=125,000 Btu
One gallon Liquefied Petroleum Gas (LPG)=91,000 Btu
One gallon Liquefied Natural Gas (LNG)=83,000 Btu
These other fuels, including, for example, diesel, gasoline, kerosene, and propane, may be used in applications similar to LNG. However, as described below with respect to embodiments of the disclosed invention, unlike LNG, these other fuels do not provide significant “cold energy.”
As a fuel, LNG is versatile and can be used in just about any way other fuels are used. These uses may be, for example, in boilers, dryers, power generation, marine fuel, locomotives, drilling rigs, asphalt plants, port operations, and over-the-road trucks. Once LNG arrives at an industrial site, it is vaporized or gasified into a gas for consumption. Prior to vaporization or gasification, LNG is not flammable and will not combust unless it is in a mixture with air where the natural gas is between 5% to 15% mixture with air. Vaporizing or gasifying LNG theoretically requires the same amount of energy from the environment as compared to the energy required to liquefy natural gas.
The amount of energy required to liquefy natural gas tends to vary with, for example, gas composition, gas pressure, product purity, product pressure, and refrigeration technology. With respect to liquefaction, for example, small scale liquefiers of less than about 500,000 gallons per day may require about 0.7 to 0.9 kWh/gallon of LNG, not including energy associated with inlet gas compressions, pretreatment, and other processes.
Conventional vaporization or gasification LNG systems and methods use various heat exchangers. The NFPA-59A Standard for Production, Storage, and Handling of Liquefied Natural Gas lists five options: (1) Ambient vaporizer, (2) Heated Vaporizer, (3) Integral Heated Vaporizer, (4) Remote Heated Vaporizer, and (5) Process Vaporizer. However, with the conventional vaporization or gasification LNG systems and methods, the cooled process fluid used to vaporize or gasify the LNG is discharged to the environment and/or the “cold energy” is not otherwise utilized.